Compressor boost stages are commonly utilized to increase an overall pressure ratio in gas turbine engines. A compressor boost stage pressurizes the air upstream of a core section of an engine and is typically part of a low pressure spool of the engine driven by at least one low pressure turbine. The coupling between the boost stage and the low pressure spool is typically at a fixed speed ratio such that the rotational speed of the boost stage may only be varied by varying the rotational speed of the low pressure spool. Hence, the fixed speed ratio between the boost stage and the low pressure spool limits the ability to vary the overall pressure ratio during operation of the engine.
Improvement in driving of compressor boost stages in gas turbine engines is therefore desirable.